Graphene-enabled anti-corrosion coating

ABSTRACT

Provided is a graphene-based aqueous coating suspension comprising multiple graphene sheets, particles of an anti-corrosive pigment or sacrificial metal, and a waterborne binder resin dissolved or dispersed in water, wherein the multiple graphene sheets contain single-layer or few-layer graphene sheets selected from a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.001% to 47% by weight of non-carbon elements wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, doped graphene, chemically functionalized graphene, or a combination thereof and wherein the coating suspension does not contain a silicate binder or microspheres dispersed therein. Also provided is an object or structure coated at least in part with such a coating.

FIELD OF THE INVENTION

The present invention relates generally to the field of anti-corrosioncoating and, more particularly, to a graphene-enabled coatingcomposition and a method of operating same.

BACKGROUND OF THE INVENTION

Corrosion of metallic materials is a costly problem. For example, thecost of corrosion-induced issues accounts for 2% to 5% of the annualgross domestic product (GDP) in the USA. Corrosions occurs to bothferrous metals (e.g. iron and steel) and non-ferrous metals (e.g.aluminum, copper, etc.). These metallic materials are commonly used inmarine and off-shore structures, bridges, containers, refineries,power-plants, storage tanks, cranes, windmills, airports, petrochemicalfacilities, etc.

Corrosion resistant coatings protect metal components againstdegradation due to moisture, salt spray, oxidation, or exposure to avariety of environmental or industrial chemicals. Anti-corrosion coatingenables added protection of metal surfaces and acts as a barrier againstthe contact between corrosive agents and the metal substrates to beprotected. In addition to corrosion prevention, many of the coatingsalso provide improved abrasion resistance, non-stick performance andchemical protection. Coatings with anti-corrosive properties ensuremetal components have the longest possible lifespan.

As an example, an anti-corrosive coating for protecting steel structuresincludes a zinc primer wherein zinc is used as a conductive pigment toproduce an anodically active coating. Zinc acts as a sacrificial anodicmaterial that protects the steel substrate, which becomes the cathode.The resistance to corrosion is presumably dependent upon the transfer ofgalvanic current by the zinc primer and the steel substrate remainsgalvanically protected provided the electrical conductivity in thesystem is maintained and there is sufficient zinc to act as the anode.In order to meet these requirements, zinc primers are typicallyformulated to contain a high loading of zinc particles (e.g. as high as80% by weight of zinc) and zinc pigment particles in zinc primers arepacked closely together. However, a high zinc loading means a high levelof difficulty in dispersing solid contents in a liquid medium,difficulty in applying the primer onto steel surfaces to be protected,excessively thick and dense coatings, and high costs. Other coatingsystems for protecting other types of metallic structures also haveserious drawbacks.

Thus, it remains highly desirable to develop improved anti-corrosioncoatings. A specific object of the present invention is a new coatingsystem that requires a lesser amount of an anodic or sacrificialmaterial.

SUMMARY OF THE INVENTION

The present invention provides a graphene-based aqueous coatingsuspension comprising multiple graphene sheets, particles of ananti-corrosive pigment or sacrificial metal, and a waterborne binderresin dissolved or dispersed in water, wherein the multiple graphenesheets contain single-layer or few-layer graphene sheets selected from apristine graphene material having essentially zero % of non-carbonelements, or a non-pristine graphene material having 0.001% to 47% byweight of non-carbon elements wherein said non-pristine graphene isselected from graphene oxide, reduced graphene oxide, graphene fluoride,graphene chloride, graphene bromide, graphene iodide, hydrogenatedgraphene, nitrogenated graphene, doped graphene, chemicallyfunctionalized graphene, or a combination thereof. The non-pristinegraphene material can have 1% to 30% by weight of non-carbon elementsselected from O, H, N, F, Cl, Br, I, B, P, or a combination thereof. Thecoating suspension does not contain microspheres (such as glass,ceramic, and polymeric microspheres). In certain embodiments, thecoating suspension does not contain a silicate binder.

In certain embodiments, the anti-corrosive pigment or sacrificial metalis selected from aluminum, chromium, zinc, beryllium, magnesium, analloy thereof, zinc phosphate, or a combination thereof.

The waterborne binder resin may preferably contain a waterbornethermoset resin selected from water-soluble or dispersible epoxy resin,water-soluble or dispersible polyurethane resin, water-soluble ordispersible urethane-urea resin, water-soluble or dispersible phenolicresin, water-soluble or dispersible acrylic resin, water-soluble ordispersible alkyd resin, or a combination thereof.

The coating suspension may further comprise other coating/paintingredients as will be apparent to a skilled person in the art. Examplesof such ingredients are fillers, additives (e.g. surfactants,dispersants, defoaming agents, catalysts, accelerators, stabilizers,coalescing agents, thixothropic agents, anti-settling agents, and dyes),coupling agents, extenders, conductive pigments, electron-conductingpolymers, or a combination thereof. Again, the coating suspension doesnot contain microspheres of glass, ceramic, or polymer, etc.

The conductive pigment may be selected from acetylene black, carbonblack, expanded graphite flake, carbon fibers, carbon nanotubes, micacoated with antimony-doped tin oxide or indium tin oxide, or a mixturethereof

The electron-conducting polymer is preferably selected from the groupconsisting of polydiacetylene, polyacetylene (PAc), polypyrrole (PPy),polyaniline (PAni), polythiophene (PTh), polyisothionaphthene (PITN),polyheteroarylenvinylene (PArV), in which the heteroarylene group can bethe thiophene, furan or pyrrole, poly-p-phenylene (PpP),polyphthalocyanine (PPhc) and the like, and their derivatives, andcombinations thereof.

In some embodiments, the chemical functional group attached tofunctionalized graphene sheets is selected from alkyl or aryl silane,alkyl or aralkyl group, hydroxyl group, carboxyl group, amine group,sulfonate group (—SO₃H), aldehydic group, quinoidal, fluorocarbon, or acombination thereof.

Alternatively, the functional group attached to graphene sheets containsa derivative of an azide compound selected from the group consisting of2-azidoethanol, 3-azidopropan-1-amine, 4-(2-azidoethoxy)-4-oxobutanoicacid, 2-azidoethyl-2-bromo-2-methylpropanoate, chlorocarbonate,azidocarbonate, dichlorocarbene, carbene, aryne, nitrene,(R-)-oxycarbonyl nitrenes, where R=any one of the following groups,derivatives thereof,

and combinations thereof.

In certain embodiments, the functional group is selected from the groupconsisting of hydroxyl, peroxide, ether, keto, and aldehyde. In certainembodiments, the functionalizing agent contains a functional groupselected from the group consisting of SO₃H, COOH, NH₂, OH, R′CHOH, CHO,CN, COCl, halide, COSH, SH, COOR′, SR′, SiR′₃, Si(—OR′—)_(y)R′₃-y,Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is aninteger equal to or less than 3, R′ is hydrogen, alkyl, aryl,cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ isfluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, Xis halide, and Z is carboxylate or trifluoroacetate, and combinationsthereof.

The functional group may be selected from the group consisting ofamidoamines, polyamides, aliphatic amines, modified aliphatic amines,cycloaliphatic amines, aromatic amines, anhydrides, ketimines,diethylenetriamine (DETA), triethylene-tetramine (TETA),tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxyadduct, phenolic hardener, non-brominated curing agent, non-aminecuratives, and combinations thereof.

In some embodiments, the functional group is selected from OY, NHY,O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, and Y is afunctional group of a protein, a peptide, an amino acid, an enzyme, anantibody, a nucleotide, an oligonucleotide, an antigen, or an enzymesubstrate, enzyme inhibitor or the transition state analog of an enzymesubstrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X,R′N⁺(R′)₃X⁻, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′,R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′,(C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than200.

The invention also provides an object or structure coated at least inpart with a coating comprising multiple graphene sheets, particles of ananti-corrosive pigment or sacrificial metal, and a waterborne binderresin that bonds the graphene sheets and the particles of ananti-corrosive pigment or sacrificial metal together and bonds them to asurface of the object or structure, wherein the multiple graphene sheetscontain single-layer or few-layer graphene sheets selected from apristine graphene material having essentially zero % of non-carbonelements, or a non-pristine graphene material having 0.001% to 47% byweight of non-carbon elements wherein the non-pristine graphene isselected from graphene oxide, reduced graphene oxide, graphene fluoride,graphene chloride, graphene bromide, graphene iodide, hydrogenatedgraphene, nitrogenated graphene, doped graphene, chemicallyfunctionalized graphene, or a combination thereof and wherein thecoating does not contain a silicate binder or microspheres dispersedtherein.

The anti-corrosive pigment or sacrificial metal in the coating may beselected from aluminum, chromium, zinc, beryllium, magnesium, an alloythereof, zinc phosphate, or a combination thereof. The coating appliedon the object or structure typically has a thickness from 1 nm to 10 mm,from typically from 10 nm to 1 mm. In certain embodiments, the object orstructure is metallic.

The coating applied on the object or structure may contain a waterbornebinder resin selected from an ester resin, a neopentyl glycol (NPG),ethylene glycol (EG), isophthalic acid, a terephthalic acid, a urethaneresin, a urethane ester resin, an urethane-urea resin, an acrylic resin,an acrylic urethane resin, derivatives thereof, or a combinationthereof.

The waterborne binder resin may contain a curing agent and/or a couplingagent in an amount of 1 to 30 parts by weight based on 100 parts byweight of the binder resin.

For the coating applied on the object or structure, the waterbornebinder resin may contain a thermally curable resin containing apolyfunctional epoxy monomer selected from diglycerol tetraglycidylether, dipentaerythritol tetraglycidyl ether, sorbitol polyglycidylether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidylether, derivatives thereof, or combinations thereof.

In certain embodiments, the waterborne binder resin contains a thermallycurable resin containing a bi- or tri-functional epoxy monomer selectedfrom the group consisting of trimethylolethane triglycidyl ether,trimethylolmethane triglycidyl ether, trimethylolpropane triglycidylether, triphenylolmethane triglycidyl ether, trisphenol triglycidylether, tetraphenylol ethane triglycidyl ether, tetraglycidyl ether oftetraphenylol ethane, p-aminophenol triglycidyl ether, 1,2,6-hexanetrioltriglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidylether, glycerol ethoxylate triglycidyl ether, castor oil triglycidylether, propoxylated glycerine triglycidyl ether, ethylene glycoldiglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycoldiglycidyl ether, cyclohexanedimethanol diglycidyl ether, dipropyleneglycol diglycidyl ether, polypropylene glycol diglycidyl ether,dibromoneopentyl glycol diglycidyl ether, hydrogenated bisphenol Adiglycidyl ether, (3,4-epoxycyclohexane) methyl3,4-epoxycylohexylcarboxylate, derivatives thereof, and mixturesthereof.

In certain embodiments, the waterborne binder resin contains an UVradiation curable resin or lacquer selected from acrylate andmethacrylate oligomers, (meth)acrylate (acrylate and methacrylate),polyhydric alcohols and their derivatives having (meth)acrylatefunctional groups, including ethoxylated trimethylolpropanetri(meth)acrylate, tripropylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, diethylene glycoldi(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritoltri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, or neopentyl glycol di(meth)acrylate and mixturesthereof, and acrylate and methacrylate oligomers derived fromlow-molecular weight polyester resin, polyether resin, epoxy resin,polyurethane resin, alkyd resin, spiroacetal resin, epoxy acrylates,polybutadiene resin, and polythiol-polyene resin.

In certain embodiments, the object or structure is a metallicreinforcing material or member. The object or structure may be aconcrete structure, a bridge.

The invention also provides a method of inhibiting corrosion of astructure or object having a surface, the method comprising coating atleast a portion of the surface with the presently invented coatingsuspension described above and at least partially removing water fromthe suspension, upon completion of the coating step.

In this method, the anti-corrosive pigment or sacrificial metal isselected from aluminum, chromium, zinc, beryllium, magnesium, an alloythereof, zinc phosphate, or a combination thereof. In the method, thewaterborne binder resin preferably contains a waterborne thermoset resinselected from water-soluble or dispersible epoxy resin, water-soluble ordispersible polyurethane resin, water-soluble or dispersible phenolicresin, water-soluble or dispersible acrylic resin, water-soluble ordispersible alkyd resin, or a combination thereof. The non-pristinegraphene material preferably has 1% to 30% by weight of non-carbonelements selected from O, H, N, F, Cl, Br, I, B, P, or a combinationthereof. The method may further comprise a carrier, filler, dispersant,surfactant, defoaming agent, catalyst, accelerator, stabilizer,coalescing agent, thixothropic agent, anti-settling agent, color dye, acoupling agent, an extender, a conductive pigment, anelectron-conducting polymer, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A flow chart showing the most commonly used process for producingoxidized graphene sheets that entails chemical oxidation/intercalation,rinsing, and high-temperature exfoliation procedures.

FIG. 2 The polarization current density vs. voltage (electrochemicalpotential) for four anti-corrosive coating compositions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a graphene-based aqueous coatingsuspension for use in protecting a metallic surface against corrosion oroxidation. This coating suspension may be applied to a metal substratesurface as a primer, a mid-coating layer, or a surface-coating layer(top-coating layer). In certain embodiments, this coating suspensioncomprises multiple graphene sheets, particles of an anti-corrosivepigment or sacrificial metal, and a waterborne binder resin dissolved ordispersed in water, wherein the multiple graphene sheets containsingle-layer or few-layer graphene sheets selected from a pristinegraphene material having essentially zero of non-carbon elements, or anon-pristine graphene material having 0.001% to 47% by weight ofnon-carbon elements wherein the non-pristine graphene is selected fromgraphene oxide, reduced graphene oxide, graphene fluoride, graphenechloride, graphene bromide, graphene iodide, hydrogenated graphene,nitrogenated graphene, doped graphene, chemically functionalizedgraphene, or a combination thereof. The non-pristine graphene materialcan have 1% to 30% by weight of non-carbon elements selected from O, H,N, F, Cl, Br, I, B, P, or a combination thereof. Preferably, the coatingsuspension does not contain microspheres (such as glass, ceramic, andpolymeric microspheres) as a filler. In certain embodiments, the coatingsuspension does not contain a silicate binder.

In a preferred or typical coating composition (upon removal of water),the resulting solid contents contain 0.1%-30% by weight of graphenesheets, 1%-70% by weight (preferably 5%-60% and further preferably 10%to 40%) of particles of an anti-corrosive pigment or sacrificial metal,and 1%-10% by weight of a waterborne binder resin. Of course, the sum ofthe three species, however formulated, must be 100%.

A conventional anti-corrosive coating for protecting steel structurestypically contains a zinc primer wherein zinc is used as a conductivepigment to produce an anodically active coating. The steel or ironsubstrate, to be protected, acts as the cathode. Zinc acts as asacrificial anodic material that protects the steel or iron substrate.The resistance to corrosion presumably relies upon the transfer ofgalvanic current by the zinc primer. The steel substrate remainsgalvanically protected provided the electron-conducting pathways in thesystem are maintained and there is sufficient zinc to act as the anode.Unfortunately, zinc primers are typically formulated to contain a highloading of zinc particles (e.g. as high as 80% by weight of zinc). Ahigh zinc loading means a high level of difficulty in dispersing solidcontents in a liquid medium, difficulty in applying the primer ontosteel surfaces to be protected, excessively thick and dense coatings,and high costs. Other coating systems for protecting other types ofmetallic structures also have serious drawbacks.

In the present invention, we have surprisingly observed that by adding1% by weight of select functionalized graphene into the zinc primer onecan curtail the Zn amount from 80% down to 20% by weight (a 4-foldreduction in Zn amount) without compromising the anti-corrosioncapability. This is a dramatic improvement in performance and is totallyunexpected. That 1% by weight graphene can completely replace 60% byweight zinc is stunning and unprecedented.

We have further observed that, in addition to zinc (or as an alternativeto zinc), other elements or compounds such as aluminum, chromium,beryllium, magnesium, an alloy thereof, zinc phosphate, or a combinationthereof can also be used as an anti-corrosive pigment or sacrificialmetal to pair up with graphene sheets. The use of a small amount ofgraphene (typically from 0.1% to 10% by weight) can replace up to 70% byweight of these anti-corrosive pigment materials.

The waterborne binder resin may preferably contain a waterbornethermoset resin selected from water-soluble or dispersible epoxy resin,water-soluble or dispersible polyurethane resin, water-soluble ordispersible phenolic resin, water-soluble or dispersible acrylic resin,water-soluble or dispersible alkyd resin, or a combination thereof.

The coating suspension may further comprise other coating/paintingredients as will be apparent to a skilled person in the art. Examplesof such ingredients are fillers, additives (e.g. surfactants,dispersants, defoaming agents, catalysts, accelerators, stabilizers,coalescing agents, thixothropic agents, anti-settling agents, and dyes),coupling agents, extenders, conductive pigments, electron-conductingpolymers, or a combination thereof. Again, the coating suspension doesnot contain microspheres of glass, ceramic, or polymer, etc. as a filleror additive.

The conductive pigment may be selected from acetylene black, carbonblack, expanded graphite flake, carbon fibers, carbon nanotubes, micacoated with antimony-doped tin oxide or indium tin oxide, or a mixturethereof

The electron-conducting polymer is preferably selected from the groupconsisting of polydiacetylene, polyacetylene (PAc), polypyrrole (PPy),polyaniline (PAni), polythiophene (PTh), polyisothionaphthene (PITN),polyheteroarylenvinylene (PArV), in which the heteroarylene group can bethe thiophene, furan or pyrrole, poly-p-phenylene (PpP),polyphthalocyanine (PPhc) and the like, and their derivatives, andcombinations thereof

Coating suspensions may be readily made by dispersing/mixing graphenesheets, particles of an anti-corrosive pigment or sacrificial metal, anda waterborne binder resin in water using well-known methods andequipment; e.g. using a disperser/mixer/homogenizer or anultrasonicator.

Coating suspension may be applied onto a substrate surface using one ofthe many well-known coating/painting methods, such as air-assistedspraying, ultrasonic spraying, painting, printing, and dip coating. Incertain embodiments, one may simply immerse or dip the metalliccomponent in the graphene-based coating suspension and then removing thecomponent from the graphene dispersion to effect deposition of graphenesheets and the binder onto a surface of the metallic component whereinthe graphene sheets are bonded to the metal surface to form a layer ofbonded graphene sheets. Alternatively, one may simply spray the coatingsuspension over the metallic component surface, allowing the watercomponent to get vaporized and the binder resin to get cured orsolidified.

The binder resin layer may be formed of an adhesive compositionincluding an adhesive resin as a main ingredient. The adhesive resincomposition may include a curing agent and a coupling agent along withthe adhesive resin. Examples of the adhesive resin may include an esterresin, a urethane resin, a urethane ester resin, an acrylic resin, andan acrylic urethane resin, specifically ester resins including neopentylglycol (NPG), ethylene glycol (EG), isophthalic acid, and terephthalicacid. The curing agent may be present in an amount of 1 to 30 parts byweight based on 100 parts by weight of the adhesive resin. The couplingagent may include epoxy silane compounds.

Curing of this binder resin may be conducted via heat, UV, or ionizingradiation. This can involve heating the heat-curable composition to atemperature of at least 70° C., preferably of 90° C. to 150° C., for atleast 1 minute (typically up to 2 hours and more typically from 2minutes to 30 minutes), so as to form a hard coating layer.

The metallic component surfaces may be brought to be in contact with thegraphene dispersion using dipping, coating (e.g. doctor-blade coating,bar coating, slot-die coating, comma coating, reversed-roll coating,etc.), roll-to-roll process, inkjet printing, screen printing,micro-contact, gravure coating, spray coating, ultrasonic spray coating,electrostatic spray coating, and flexographic printing. The thickness ofthe hard coat layer is generally about 1 nm to 1 mm, preferably 10 nm to100 μm, and most preferably 100 nm to 10 μm.

For thermally curable resins, the polyfunctional epoxy monomer may beselected preferably from diglycerol tetraglycidyl ether,dipentaerythritol tetraglycidyl ether, sorbitol polyglycidyl ether,polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether(e.g. pentaerythritol tetraglycidyl ether), or a combination thereof.The bi- or tri-functional epoxy monomer can be selected from the groupconsisting of trimethylolethane triglycidyl ether, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether,triphenylolmethane triglycidyl ether, trisphenol triglycidyl ether,tetraphenylol ethane triglycidyl ether, tetraglycidyl ether oftetraphenylol ethane, p-aminophenol triglycidyl ether, 1,2,6-hexanetrioltriglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidylether, glycerol ethoxylate triglycidyl ether, castor oil triglycidylether, propoxylated glycerine triglycidyl ether, ethylene glycoldiglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycoldiglycidyl ether, cyclohexanedimethanol diglycidyl ether, dipropyleneglycol diglycidyl ether, polypropylene glycol diglycidyl ether,dibromoneopentyl glycol diglycidyl ether, hydrogenated bisphenol Adiglycidyl ether, (3,4-epoxycyclohexane) methyl3,4-epoxycylohexylcarboxylate, derivatives thereof, and mixturesthereof.

In certain embodiments, the heat-curable compositions of the presentinvention advantageously further contain small amounts, preferably from0.05 to 0.20% by weight, of at least one surface active compound. Thesurface active agent is important for good wetting of the substrateresulting in satisfactory final hard-coating.

The UV radiation curable resins and lacquers usable for the binder resinin this invention include those derived from photo polymerizablemonomers and oligomers, such as acrylate and methacrylate oligomers (theterm “(meth)acrylate” used herein refers to acrylate and methacrylate),of polyfunctional compounds, such as polyhydric alcohols and theirderivatives having (meth)acrylate functional groups such as ethoxylatedtrimethylolpropane tri(meth)acrylate, tripropylene glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, diethyleneglycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate,pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate,1,6-hexanediol di(meth)acrylate, or neopentyl glycol di(meth)acrylateand mixtures thereof, and acrylate and methacrylate oligomers derivedfrom low-molecular weight polyester resin, polyether resin, epoxy resin,polyurethane resin, alkyd resin, spiroacetal resin, epoxy acrylates,polybutadiene resin, and polythiol-polyene resin.

The UV polymerizable monomers and oligomers are coated (e.g. afterretreating from dipping) and dried, and subsequently exposed to UVradiation to form an optically clear cross-linked abrasion resistantlayer. The preferred UV cure dosage is between 50 and 1000 mJ/cm².

UV-curable resins are typically ionizing radiation-curable as well. Theionizing radiation-curable resins may contain a relatively large amountof a reactive diluent. Reactive diluents usable herein includemonofunctional monomers, such as ethyl (meth)acrylate, ethylhexyl(meth)acrylate, styrene, vinyl toluene, and N-vinylpyrrolidone, andpolyfunctional monomers, for example, trimethylolpropanetri(meth)acrylate, hexanediol (meth)acrylate, tripropylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritoltri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, derivativesthereof, and combinations thereof.

The aforementioned binder resins are normally solvent-based, beinginitially soluble in an organic solvent (prior to being cured orcross-linked). However, most of the monomers or polymers (prior tocuring) in these binder resins can be chemically modified (e.g.carboxylated, hydroxylated, or somehow functionalized) to become solubleor dispersible in water. They then become ingredients of waterbornecoating systems. There are intrinsically water-soluble orwater-dispersible resin systems that are commercially available.

The preparation of graphene sheets and graphene dispersions is describedas follows: Carbon is known to have five unique crystalline structures,including diamond, fullerene (0-D nanographitic material), carbonnanotube or carbon nanofiber (1-D nanographitic material), graphene (2-Dnanographitic material), and graphite (3-D graphitic material). Thecarbon nanotube (CNT) refers to a tubular structure grown with a singlewall or multi-wall. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs)have a diameter on the order of a few nanometers to a few hundrednanometers. Their longitudinal, hollow structures impart uniquemechanical, electrical and chemical properties to the material. The CNTor CNF is a one-dimensional nanocarbon or 1-D nanographite material.

Our research group pioneered the development of graphene materials andrelated production processes as early as 2002: (1) B. Z. Jang and W. C.Huang, “Nano-scaled Graphene Plates,” U.S. Pat. No. 7,071,258 (Jul. 4,2006), application submitted on Oct. 21, 2002; (2) B. Z. Jang, et al.“Process for Producing Nano-scaled Graphene Plates,” U.S. patentapplication Ser. No. 10/858,814 (Jun. 3, 2004) (U.S. Patent Pub. No.2005/0271574); and (3) B. Z. Jang, A. Zhamu, and J. Guo, “Process forProducing Nano-scaled Platelets and Nanocomposites,” U.S. patentapplication Ser. No. 11/509,424 (Aug. 25, 2006) (U.S. Patent Pub. No.2008-0048152).

A single-layer graphene sheet is composed of carbon atoms occupying atwo-dimensional hexagonal lattice. Multi-layer graphene is a plateletcomposed of more than one graphene plane. Individual single-layergraphene sheets and multi-layer graphene platelets are hereincollectively called nanographene platelets (NGPs) or graphene materials.NGPs include pristine graphene (essentially 99% of carbon atoms),slightly oxidized graphene (<5% by weight of oxygen), graphene oxide(≥5% by weight of oxygen), slightly fluorinated graphene (<5% by weightof fluorine), graphene fluoride ((≥5% by weight of fluorine), otherhalogenated graphene, and chemically functionalized graphene.

NGPs have been found to have a range of unusual physical, chemical, andmechanical properties. For instance, graphene was found to exhibit thehighest intrinsic strength and highest thermal conductivity of allexisting materials. Although practical electronic device applicationsfor graphene (e.g., replacing Si as a backbone in a transistor) are notenvisioned to occur within the next 5-10 years, its application as ananofiller in a composite material and an electrode material in energystorage devices is imminent. The availability of processable graphenesheets in large quantities is essential to the success in exploitingcomposite, energy, and other applications for graphene.

The processes for producing NGPs and NGP nanocomposites were reviewed byus [Bor Z. Jang and A Zhamu, “Processing of Nano Graphene Platelets(NGPs) and NGP Nanocomposites: A Review,” J. Materials Sci. 43 (2008)5092-5101].

A highly useful approach (FIG. 1 ) entails treating natural graphitepowder with an intercalant and an oxidant (e.g., concentrated sulfuricacid and nitric acid, respectively) to obtain a graphite intercalationcompound (GIC) or, actually, graphite oxide (GO). [William S. Hummers,Jr., et al., Preparation of Graphitic Oxide, Journal of the AmericanChemical Society, 1958, p. 1339.] Prior to intercalation or oxidation,graphite has an inter-graphene plane spacing of approximately 0.335 nm(L_(d)=½ d₀₀₂=0.335 nm). With an intercalation and oxidation treatment,the inter-graphene spacing is increased to a value typically greaterthan 0.6 nm. This is the first expansion stage experienced by thegraphite material during this chemical route. The obtained GIC or GO isthen subjected to further expansion (often referred to as exfoliation)using either a thermal shock exposure or a solution-based,ultrasonication-assisted graphene layer exfoliation approach.

In the thermal shock exposure approach, the GIC or GO is exposed to ahigh temperature (typically 800-1,050° C.) for a short period of time(typically 15 to 60 seconds) to exfoliate or expand the GIC or GO forthe formation of exfoliated or further expanded graphite, which istypically in the form of a “graphite worm” composed of graphite flakesthat are still interconnected with one another. This thermal shockprocedure can produce some separated graphite flakes or graphene sheets,but normally the majority of graphite flakes remain interconnected.Typically, the exfoliated graphite or graphite worm is then subjected toa flake separation treatment using air milling, mechanical shearing, orultrasonication in water. Hence, approach 1 basically entails threedistinct procedures: first expansion (oxidation or intercalation),further expansion (or “exfoliation”), and separation.

In the solution-based separation approach, the expanded or exfoliated GOpowder is dispersed in water or aqueous alcohol solution, which issubjected to ultrasonication. It is important to note that in theseprocesses, ultrasonification is used after intercalation and oxidationof graphite (i.e., after first expansion) and typically after thermalshock exposure of the resulting GIC or GO (after second expansion).Alternatively, the GO powder dispersed in water is subjected to an ionexchange or lengthy purification procedure in such a manner that therepulsive forces between ions residing in the inter-planar spacesovercome the inter-graphene van der Waals forces, resulting in graphenelayer separations.

In the aforementioned examples, the starting material for thepreparation of graphene sheets or NGPs is a graphitic material that maybe selected from the group consisting of natural graphite, artificialgraphite, graphite oxide, graphite fluoride, graphite fiber, carbonfiber, carbon nanofiber, carbon nanotube, mesophase carbon micro-bead(MCMB) or carbonaceous micro-sphere (CMS), soft carbon, hard carbon, andcombinations thereof.

Graphite oxide may be prepared by dispersing or immersing a laminargraphite material (e.g., powder of natural flake graphite or syntheticgraphite) in an oxidizing agent, typically a mixture of an intercalant(e.g., concentrated sulfuric acid) and an oxidant (e.g., nitric acid,hydrogen peroxide, sodium perchlorate, potassium permanganate) at adesired temperature (typically 0-70° C.) for a sufficient length of time(typically 4 hours to 5 days). The resulting graphite oxide particlesare then rinsed with water several times to adjust the pH values totypically 2-5. The resulting suspension of graphite oxide particlesdispersed in water is then subjected to ultrasonication to produce adispersion of separate graphene oxide sheets dispersed in water. A smallamount of reducing agent (e.g. Na₄B) may be added to obtain reducedgraphene oxide (RDO) sheets.

In order to reduce the time required to produce a precursor solution orsuspension, one may choose to oxidize the graphite to some extent for ashorter period of time (e.g., 30 minutes-4 hours) to obtain graphiteintercalation compound (GIC). The GIC particles are then exposed to athermal shock, preferably in a temperature range of 600-1,100° C. fortypically 15 to 60 seconds to obtain exfoliated graphite or graphiteworms, which are optionally (but preferably) subjected to mechanicalshearing (e.g. using a mechanical shearing machine or an ultrasonicator)to break up the graphite flakes that constitute a graphite worm. Eitherthe already separated graphene sheets (after mechanical shearing) or theun-broken graphite worms or individual graphite flakes are thenre-dispersed in water, acid, or organic solvent and ultrasonicated toobtain a graphene dispersion.

The pristine graphene material is preferably produced by one of thefollowing three processes: (A) Intercalating the graphitic material witha non-oxidizing agent, followed by a thermal or chemical exfoliationtreatment in a non-oxidizing environment; (B) Subjecting the graphiticmaterial to a supercritical fluid environment for inter-graphene layerpenetration and exfoliation; or (C) Dispersing the graphitic material ina powder form to an aqueous solution containing a surfactant ordispersing agent to obtain a suspension and subjecting the suspension todirect ultrasonication to obtain a graphene dispersion.

In Procedure (A), a particularly preferred step comprises (i)intercalating the graphitic material with a non-oxidizing agent,selected from an alkali metal (e.g., potassium, sodium, lithium, orcesium), alkaline earth metal, or an alloy, mixture, or eutectic of analkali or alkaline metal; and (ii) a chemical exfoliation treatment(e.g., by immersing potassium-intercalated graphite in ethanolsolution).

In Procedure (B), a preferred step comprises immersing the graphiticmaterial to a supercritical fluid, such as carbon dioxide (e.g., attemperature T>31° C. and pressure P>7.4 MPa) and water (e.g., at T>374°C. and P>22.1 MPa), for a period of time sufficient for inter-graphenelayer penetration (tentative intercalation). This step is then followedby a sudden de-pressurization to exfoliate individual graphene layers.Other suitable supercritical fluids include methane, ethane, ethylene,hydrogen peroxide, ozone, water oxidation (water containing a highconcentration of dissolved oxygen), or a mixture thereof.

In Procedure (C), a preferred step comprises (a) dispersing particles ofa graphitic material in a liquid medium containing therein a surfactantor dispersing agent to obtain a suspension or slurry; and (b) exposingthe suspension or slurry to ultrasonic waves (a process commonlyreferred to as ultrasonication) at an energy level for a sufficientlength of time to produce a graphene dispersion of separated graphenesheets (non-oxidized NGPs) dispersed in a liquid medium (e.g. water,alcohol, or organic solvent).

NGPs can be produced with an oxygen content no greater than 25% byweight, preferably below 20% by weight, further preferably below 5%.Typically, the oxygen content is between 5% and 20% by weight. Theoxygen content can be determined using chemical elemental analysisand/or X-ray photoelectron spectroscopy (XPS).

The laminar graphite materials used in the prior art processes for theproduction of the GIC, graphite oxide, and subsequently made exfoliatedgraphite, flexible graphite sheets, and graphene platelets were, in mostcases, natural graphite. However, the present invention is not limitedto natural graphite. The starting material may be selected from thegroup consisting of natural graphite, artificial graphite (e.g., highlyoriented pyrolytic graphite, HOPG), graphite oxide, graphite fluoride,graphite fiber, carbon fiber, carbon nanofiber, carbon nanotube,mesophase carbon micro-bead (MCMB) or carbonaceous micro-sphere (CMS),soft carbon, hard carbon, and combinations thereof. All of thesematerials contain graphite crystallites that are composed of layers ofgraphene planes stacked or bonded together via van der Waals forces. Innatural graphite, multiple stacks of graphene planes, with the grapheneplane orientation varying from stack to stack, are clustered together.In carbon fibers, the graphene planes are usually oriented along apreferred direction. Generally speaking, soft carbons are carbonaceousmaterials obtained from carbonization of liquid-state, aromaticmolecules. Their aromatic ring or graphene structures are more or lessparallel to one another, enabling further graphitization. Hard carbonsare carbonaceous materials obtained from aromatic solid materials (e.g.,polymers, such as phenolic resin and polyfurfuryl alcohol). Theirgraphene structures are relatively randomly oriented and, hence, furthergraphitization is difficult to achieve even at a temperature higher than2,500° C. But, graphene sheets do exist in these carbons.

Fluorinated graphene or graphene fluoride is herein used as an exampleof the halogenated graphene material group. There are two differentapproaches that have been followed to produce fluorinated graphene: (1)fluorination of pre-synthesized graphene: This approach entails treatinggraphene prepared by mechanical exfoliation or by CVD growth withfluorinating agent such as XeF₂, or F-based plasmas; (2) Exfoliation ofmultilayered graphite fluorides: Both mechanical exfoliation and liquidphase exfoliation of graphite fluoride can be readily accomplished [F.Karlicky, et al. “Halogenated Graphenes: Rapidly Growing Family ofGraphene Derivatives” ACS Nano, 2013, 7 (8), pp 6434-6464].

Interaction of F₂ with graphite at high temperature leads to covalentgraphite fluorides (CF)_(n) or (C₂F)_(n), while at low temperaturesgraphite intercalation compounds (GIC) C_(x)F (2≤x≤24) form. In (CF)_(n)carbon atoms are sp3-hybridized and thus the fluorocarbon layers arecorrugated consisting of trans-linked cyclohexane chairs. In (C₂F)_(n)only half of the C atoms are fluorinated and every pair of the adjacentcarbon sheets are linked together by covalent C—C bonds. Systematicstudies on the fluorination reaction showed that the resulting F/C ratiois largely dependent on the fluorination temperature, the partialpressure of the fluorine in the fluorinating gas, and physicalcharacteristics of the graphite precursor, including the degree ofgraphitization, particle size, and specific surface area. In addition tofluorine (F₂), other fluorinating agents may be used, although most ofthe available literature involves fluorination with F₂ gas, sometimes inpresence of fluorides.

For exfoliating a layered precursor material to the state of individualsingle graphene layers or few-layers, it is necessary to overcome theattractive forces between adjacent layers and to further stabilize thelayers. This may be achieved by either covalent modification of thegraphene surface by functional groups or by non-covalent modificationusing specific solvents, surfactants, polymers, or donor-acceptoraromatic molecules. The process of liquid phase exfoliation includesultra-sonic treatment of a graphite fluoride in a liquid medium toproduce graphene fluoride sheets dispersed in the liquid medium. Theresulting dispersion can be directly used in the graphene deposition ofpolymer component surfaces.

The nitrogenation of graphene can be conducted by exposing a graphenematerial, such as graphene oxide, to ammonia at high temperatures(200-400° C.). Nitrogenated graphene could also be formed at lowertemperatures by a hydrothermal method; e.g. by sealing GO and ammonia inan autoclave and then increased the temperature to 150-250° C. Othermethods to synthesize nitrogen doped graphene include nitrogen plasmatreatment on graphene, arc-discharge between graphite electrodes in thepresence of ammonia, ammonolysis of graphene oxide under CVD conditions,and hydrothermal treatment of graphene oxide and urea at differenttemperatures.

For the purpose of defining the claims of the instant application, NGPsor graphene materials include discrete sheets/platelets of single-layerand multi-layer (typically less than 10 layers, the few-layer graphene)pristine graphene, graphene oxide, reduced graphene oxide (RGO),graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, doped graphene (e.g. doped by B or N). Pristine graphene hasessentially 0% oxygen. RGO typically has an oxygen content of 0.001%-5%by weight. Graphene oxide (including RGO) can have 0.001%-50% by weightof oxygen. Other than pristine graphene, all the graphene materials have0.001%-50% by weight of non-carbon elements (e.g. O, H, N, B, F, Cl, Br,I, etc.). These materials are herein referred to as non-pristinegraphene materials. The presently invented graphene can contain pristineor non-pristine graphene and the invented method allows for thisflexibility. These graphene sheets all can be chemically functionalized.

Graphene sheets have a significant proportion of edges that correspondto the edge planes of graphite crystals. The carbon atoms at the edgeplanes are reactive and must contain some heteroatom or group to satisfycarbon valency. Further, there are many types of functional groups (e.g.hydroxyl and carboxylic) that are naturally present at the edge orsurface of graphene sheets produced through chemical or electrochemicalmethods. Many chemical function groups (e.g. —NH₂, etc.) can be readilyimparted to graphene edges and/or surfaces using methods that arewell-known in the art.

In one preferred embodiment, the resulting functionalized graphenesheets (NGP) may broadly have the following formula(e): [NGP]-R_(m),wherein m is the number of different functional group types (typicallybetween 1 and 5), R is selected from SO₃H, COOH, NH₂, OH, R′CHOH, CHO,CN, COCl, halide, COSH, SH, COOR′, SR′, SiR′₃, Si(—OR′—)_(y)R′₃-y,Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is aninteger equal to or less than 3, R′ is hydrogen, alkyl, aryl,cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ isfluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, Xis halide, and Z is carboxylate or trifluoroacetate.

A commonly used curing agent for epoxy resin is diethylenetriamine(DETA), which has three —NH₂ groups. If DETA is included in theimpacting chamber, one of the three —NH₂ groups may be bonded to theedge or surface of a graphene sheet and the remaining two un-reacted—NH₂ groups will be available for reacting with epoxy resin later. Suchan arrangement provides a good interfacial bonding between the NGP(graphene sheets) and the epoxy-based binder resin.

Other useful chemical functional groups or reactive molecules may beselected from the group consisting of amidoamines, polyamides, aliphaticamines, modified aliphatic amines, cycloaliphatic amines, aromaticamines, anhydrides, ketimines, diethylenetriamine (DETA),triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA),hexamethylenetetramine, polyethylene polyamine, polyamine epoxy adduct,phenolic hardener, non-brominated curing agent, non-amine curatives,derivatives thereof, and combinations thereof. These functional groupsare multi-functional, with the capability of reacting with at least twochemical species from at least two ends. Most importantly, they arecapable of bonding to the edge or surface of graphene using one of theirends and, during subsequent epoxy curing stage, are able to react withepoxide or epoxy resin at one or two other ends.

The above-described [NGP]-R_(m) may be further functionalized. Theresulting graphene sheets include compositions of the formula:[NGP]-A_(m), where A is selected from OY, NHY, O═C—OY, P═C—NR′Y, O═C—SY,O═C—Y, —CR′1-OY, N′Y or C′Y, and Y is an appropriate functional group ofa protein, a peptide, an amino acid, an enzyme, an antibody, anucleotide, an oligonucleotide, an antigen, or an enzyme substrate,enzyme inhibitor or the transition state analog of an enzyme substrateor is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X, R′N⁺(R′)₃X⁻,R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′, R′—R″, R′—N—CO,(C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′, (C₃H₆O)_(w)—R′, R′, andw is an integer greater than one and less than 200. CNTs may besimilarly functionalized.

The NGPs and conductive additives (e.g. carbon nanofibers) may also befunctionalized to produce compositions having the formula:[NGP]-[R′-A]_(m), where m, R′ and A are as defined above. Thecompositions of the invention also include NGPs upon which certaincyclic compounds are adsorbed. These include compositions of matter ofthe formula: [NGP]-[X—R_(a)]_(m), where a is zero or a number less than10, X is a polynuclear aromatic, polyheteronuclear aromatic ormetallopolyheteronuclear aromatic moiety and R is as defined above.Preferred cyclic compounds are planar. More preferred cyclic compoundsfor adsorption are porphyrins and phthalocyanines. The adsorbed cycliccompounds may be functionalized. Such compositions include compounds ofthe formula, [NGP]-[X-A_(a)]_(m), where m, a, X and A are as definedabove.

The functionalized NGPs of the instant invention can be directlyprepared by sulfonation, or electrophilic addition to deoxygenatedgraphene platelet surfaces. The graphene platelets can be processedprior to being contacted with a functionalizing agent. Such processingmay include dispersing the graphene platelets in a solvent. In someinstances, the platelets or may then be filtered and dried prior tocontact. One particularly useful type of functional group is thecarboxylic acid moieties, which naturally exist on the surfaces of NGPsif they are prepared from the acid intercalation route discussedearlier. If carboxylic acid functionalization is needed, the NGPs may besubjected to chlorate, nitric acid, or ammonium persulfate oxidation.

Carboxylic acid functionalized graphene sheets or platelets areparticularly useful because they can serve as the starting point forpreparing other types of functionalized NGPs. For example, alcohols oramides can be easily linked to the acid to give stable esters or amides.If the alcohol or amine is part of a di- or poly-functional molecule,then linkage through the O— or NH— leaves the other functionalities aspendant groups. These reactions can be carried out using any of themethods developed for esterifying or aminating carboxylic acids withalcohols or amines as known in the art. Examples of these methods can befound in G. W. Anderson, et al., J. Amer. Chem. Soc. 86, 1839 (1964),which is hereby incorporated by reference in its entirety. Amino groupscan be introduced directly onto graphitic platelets by treating theplatelets with nitric acid and sulfuric acid to obtain nitratedplatelets, then chemically reducing the nitrated form with a reducingagent, such as sodium dithionite, to obtain amino-functionalizedplatelets.

In some embodiments, the chemically functionalized graphene sheetscontain a chemical functional group selected from alkyl or aryl silane,alkyl or aralkyl group, hydroxyl group, carboxyl group, amine group,sulfonate group (—SO₃H), aldehydic group, quinoidal, fluorocarbon, or acombination thereof. Alternatively, the functional group contains aderivative of an azide compound selected from the group consisting of2-azidoethanol, 3-azidopropan-1-amine, 4-(2-azidoethoxy)-4-oxobutanoicacid, 2-azidoethyl-2-bromo-2-methylpropanoate, chlorocarbonate,azidocarbonate, dichlorocarbene, carbene, aryne, nitrene,(R-)-oxycarbonyl nitrenes, where R=any one of the following groups,derivatives thereof,

and combinations thereof.

In certain embodiments, the functional group is selected from the groupconsisting of hydroxyl, peroxide, ether, keto, and aldehyde. In certainembodiments, the functionalizing agent contains a functional groupselected from the group consisting of SO₃H, COOH, NH₂, OH, R′CHOH, CHO,CN, COCl, halide, COSH, SH, COOR′, SR′, SiR′₃, Si(—OR′—)_(y)R′₃-y,Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is aninteger equal to or less than 3, R′ is hydrogen, alkyl, aryl,cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ isfluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, Xis halide, and Z is carboxylate or trifluoroacetate, derivativesthereof, and combinations thereof.

The functional group may be selected from the group consisting ofamidoamines, polyamides, aliphatic amines, modified aliphatic amines,cycloaliphatic amines, aromatic amines, anhydrides, ketimines,diethylenetriamine (DETA), triethylene-tetramine (TETA),tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxyadduct, phenolic hardener, non-brominated curing agent, non-aminecuratives, derivatives thereof, and combinations thereof.

In some embodiments, the functional group may be selected from OY, NHY,O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, and Y is afunctional group of a protein, a peptide, an amino acid, an enzyme, anantibody, a nucleotide, an oligonucleotide, an antigen, or an enzymesubstrate, enzyme inhibitor or the transition state analog of an enzymesubstrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X,R′N⁺(R′)₃X⁻, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′,R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′,(C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than200.

The graphene dispersions produced may be further added with an acid, ametal salt, an oxidizer, or a combination thereof to prepare a morereactive dispersion for use in the graphene coating of a metalliccomponent. One may simply dip a metallic component into the graphenesuspension for a period of several seconds to several minutes(preferably 5 seconds to 15 minutes) and then retreat the polymercomponent from the graphene-liquid dispersion. Upon removal of theliquid (e.g. via natural or forced vaporization), graphene sheets arenaturally coated on and bonded to polymer component surfaces.

The anti-corrosion coating systems were characterized by using methodsthat are well-known in the art; e.g. the salt spray test (SST) accordingto ASTM B117 (ISO 9277) and the cyclic voltammetry test (current densityvs. voltage) to obtain the cathode and anode polarization currents, etc.

The following examples are used to illustrate some specific detailsabout the best modes of practicing the instant invention and should notbe construed as limiting the scope of the invention.

Example 1: Graphene Oxide from Sulfuric Acid Intercalation andExfoliation of MCMBs

MCMB (mesocarbon microbeads) were supplied by China Steel Chemical Co.This material has a density of about 2.24 g/cm³ with a median particlesize of about 16 μm. MCMBs (10 grams) were intercalated with an acidsolution (sulfuric acid, nitric acid, and potassium permanganate at aratio of 4:1:0.05) for 48 hours. Upon completion of the reaction, themixture was poured into deionized water and filtered. The intercalatedMCMBs were repeatedly washed in a 5% solution of HCl to remove most ofthe sulfate ions. The sample was then washed repeatedly with deionizedwater until the pH of the filtrate was neutral. The slurry was dried andstored in a vacuum oven at 60° C. for 24 hours. The dried powder samplewas placed in a quartz tube and inserted into a horizontal tube furnacepre-set at a desired temperature, 800° C.-1,100° C. for 30-90 seconds toobtain graphene sheets. A quantity of graphene sheets was mixed withwater and ultrasonicated at 60-W power for 10 minutes to obtain agraphene dispersion.

A small amount was sampled out, dried, and investigated with TEM, whichindicated that most of the NGPs were between 1 and 10 layers. The oxygencontent of the graphene powders (GO or RGO) produced was from 0.1% toapproximately 25%, depending upon the exfoliation temperature and time.

Several graphene dispersions were separately added with a variety ofanti-corrosion metals, other pigments and ingredients to produce variousanti-corrosion coating compositions.

Example 2: Oxidation and Exfoliation of Natural Graphite

Graphite oxide was prepared by oxidation of graphite flakes withsulfuric acid, sodium nitrate, and potassium permanganate at a ratio of4:1:0.05 at 30° C. for 48 hours, according to the method of Hummers[U.S. Pat. No. 2,798,878, Jul. 9, 1957]. Upon completion of thereaction, the mixture was poured into deionized water and filtered. Thesample was then washed with 5% HCl solution to remove most of thesulfate ions and residual salt and then repeatedly rinsed with deionizedwater until the pH of the filtrate was approximately 4. The intent wasto remove all sulfuric and nitric acid residue out of graphiteinterstices. The slurry was dried and stored in a vacuum oven at 60° C.for 24 hours.

The dried, intercalated (oxidized) compound was exfoliated by placingthe sample in a quartz tube that was inserted into a horizontal tubefurnace pre-set at 1,050° C. to obtain highly exfoliated graphite. Theexfoliated graphite was dispersed in water along with a 1% surfactant at45° C. in a flat-bottomed flask and the resulting suspension wassubjected to ultrasonication for a period of 15 minutes to obtaindispersion of graphene oxide (GO) sheets.

Example 3: Preparation of Pristine Graphene

Pristine graphene sheets were produced by using the directultrasonication or liquid-phase exfoliation process. In a typicalprocedure, five grams of graphite flakes, ground to approximately 20 μmin sizes, were dispersed in 1,000 mL of deionized water (containing 0.1%by weight of a dispersing agent, Zonyl® FSO from DuPont) to obtain asuspension. An ultrasonic energy level of 85 W (Branson S450Ultrasonicator) was used for exfoliation, separation, and size reductionof graphene sheets for a period of 15 minutes to 2 hours. The resultinggraphene sheets were pristine graphene that had never been oxidized andwere oxygen-free and relatively defect-free.

Examples 4: Preparation of Graphene Fluoride

Several processes have been used by us to produce GF, but only oneprocess is herein described as an example. In a typical procedure,highly exfoliated graphite (HEG) was prepared from intercalated compoundC₂F.xClF₃. HEG was further fluorinated by vapors of chlorine trifluorideto yield fluorinated highly exfoliated graphite (FHEG). A pre-cooledTeflon reactor was filled with 20-30 mL of liquid pre-cooled ClF₃, andthen the reactor was closed and cooled to liquid nitrogen temperature.Subsequently, no more than 1 g of HEG was put in a container with holesfor ClF₃ gas to access the reactor. After 7-10 days, a gray-beigeproduct with approximate formula C₂F was formed. GF sheets were thendispersed in halogenated solvents to form suspensions.

Example 5: Preparation of Nitrogenated Graphene

Graphene oxide (GO), synthesized in Example 2, was finely ground withdifferent proportions of urea and the pelletized mixture heated in amicrowave reactor (900 W) for 30 s. The product was washed several timeswith deionized water and vacuum dried. In this method graphene oxidegets simultaneously reduced and doped with nitrogen. The productsobtained with graphene/urea mass ratios of 1/0.5, 1/1 and 1/2 aredesignated as N-1, N-2 and N-3 respectively and the nitrogen contents ofthese samples were 14.7, 18.2 and 17.5 wt. % respectively as determinedby elemental analysis. These nitrogenated graphene sheets remaindispersible in water.

Example 6: Functionalized Graphene as an Anti-Corrosive Ingredient

Chemical functional groups involved in this study include an azidecompound (2-azidoethanol), alkyl silane, hydroxyl group, carboxyl group,amine group, sulfonate group (—SO₃H), and diethylenetriamine (DETA).These functionalized graphene sheets are supplied from Taiwan GrapheneCo., Taipei, Taiwan. Upon removal of water and cured at 150° C. for 15minutes, graphene sheets were well bonded to metallic surfaces.

We have observed that, in general, the metallic component surfaces canbe well-bonded to the presently invented functionalized graphene sheetswith a waterborne binder resin. The coated surfaces are generallysmoother if functionalized graphene sheets are included as ananti-corrosive pigment, along with an anodic metal such as Zn or Al, ascompared to the use of the metal pigments alone.

Example 7: Polyurethane-Based Waterborne Binder Resin

Several hydroxyl/carboxyl functional polyurethane dispersions wereprepared by a non-isocyanate process according to Scheme 1 shown below:

The polymers were synthesized by first reacting the di-ester with thepolyol in the presence of an organometallic catalyst at 200°-220° C. invacuum. Methanol was the byproduct of the trans-esterification reaction.Subsequently, a hydroxyl-functional urethane diol was added, andpropylene glycol was removed in vacuum at 180° C. Thehydroxyl-functional urethane diol was prepared by a non-isocyanateprocess utilizing the reaction between a cyclic carbonate and a diamine.The resin was then carboxyl-functionalized and dispersed in water withthe aid of a neutralizing tertiary amine. Number average molecularweights for the polyurethane dispersions were in the range ofapproximately 3000-4000 g/mole.

Example 8: Polyurethane-Urea Copolymer-Based Waterborne Binder Resin

Two polyurethane-urea dispersions were prepared by the prepolymerisocyanate process given in Scheme 2. This process actually produces apolyurethane-urea polymer. The chain extension reaction of theisocyanate terminated polyurethane with the diamine forms the ureamoiety.

A melamine resin used as a cross-linker was a commercially availableversion of hexakis(methoxymethyl)melamine (HMMM), which has a degree ofpolymerization of about 1.5, an average molecular weight of 554, and anaverage theoretical functionality of 8.3. The waterborne acrylicdispersion used for formulating was Acrysol WS-68 from Rohm and Haas, ahydroxyl/carboxyl functional resin. A water-dispersible polyisocyanatefrom Bayer Corporation (Bayhydur XP-7007, a modified aliphaticisocyanate trimer) was used for crosslinking.

Example 9: Water-Soluble Alkyd Resin

In a typical procedure, a vessel equipped with a stirrer, a temperaturecontroller and a decanter was charged with the following raw materialsand the charge was heated with stirring: soybean fatty acid (33% byweight), trimethylolpropane (33%), trimellitic anhydride (8.5%),isophthalic acid 24%, dibutyltin oxide (0.5%), and xylene (1%). Waterwas formed as the reaction progressed and was removed azeotropicallywith the xylene. Heating was continued until an acid value of 39 and ahydroxyl value of 140 were attained. The reaction was then discontinued.The reaction mixture was diluted with butyl cellulosic to a non-volatilecontent of 70% by weight to give an alkyd resin varnish. This resinvarnish was neutralized with triethylamine and adjusted to anon-volatile content of 40% by weight with deionized water to give awater-soluble alkyd resin varnish. This varnish had an effective acidvalue of 33.

Example 10: Waterborne Epoxy Resin

The waterborne epoxy used in this study was based on the “1-type” (epoxyequivalent weight of about 500-600) solid epoxy dispersion, and ahydrophobic amine adduct curing agent. Both components utilize anon-ionic surfactant that is pre-reacted into the epoxy and aminecomponents. An example of such a waterborne epoxy was EPI-REZ 6520(Hexion Specialty Chemicals Co.) with EPIKURE 6870 (modified polyamineadduct).

Some representative testing results are summarized in FIG. 2 , whichindicates that adding 1% by weight of select functionalized graphenesheets (single-layer graphene) into the zinc primer allows for reductionof the required Zn amount from 80% down to 20% by weight (a 4-foldreduction in Zn amount) without compromising the anti-corrosioncapability. That 1% by weight of single-layer graphene can completelyreplace 60% by weight zinc is stunning and unprecedented. Also, 10% byweight of few-layer graphene can effectively replace 70% by weight ofZn. These dramatic improvements in performance are truly unexpected.

We have further observed that, in addition to zinc (or as an alternativeto zinc), other elements or compounds such as aluminum, chromium,beryllium, magnesium, an alloy thereof, zinc phosphate, or a combinationthereof can also be used as an anti-corrosive pigment or sacrificialmetal to pair up with various types of graphene sheets. The use of asmall amount of graphene (typically from 0.1% to 10% by weight) canreplace up to 70% by weight of these anti-corrosive pigment materials.

We claim:
 1. A graphene-based aqueous coating suspension comprising multiple graphene sheets, particles of an anti-corrosive pigment or sacrificial metal, and a waterborne binder resin dissolved or dispersed in water, wherein said multiple graphene sheets contain single-layer or few-layer graphene sheets selected from a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.001% to 47% by weight of non-carbon elements wherein said non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, doped graphene, chemically functionalized graphene, or a combination thereof and wherein said coating suspension does not contain a silicate binder or microspheres dispersed therein and wherein said graphene sheets have a weight fraction from 0.1% to 30% based on the total coating suspension weight excluding water, wherein said waterborne binder resin contains a waterborne thermoset resin selected from water-soluble or dispersible phenolic resin; wherein the suspension further includes an electron-conducting polymer selected from the group consisting of polydiacetylene, polyacetylene (PAc), polyisothionaphthene (PITN), poly-p-phenylene (PpP), polyphthalocyanine (PPhc), and their derivatives, and combinations thereof.
 2. The coating suspension of claim 1, wherein said non-pristine graphene material has 1% to 30% by weight of non-carbon elements selected from O, H, N, F, Cl, Br, I, B, P, or a combination thereof.
 3. The coating suspension of claim 1, further comprising a carrier, filler, dispersant, surfactant, defoaming agent, catalyst, accelerator, stabilizer, coalescing agent, thixothropic agent, anti-settling agent, color dye, a coupling agent, an extender, a conductive pigment, or a combination thereof.
 4. The coating suspension of claim 3, wherein said conductive pigment is selected from acetylene black, carbon black, expanded graphite flake, carbon fibers, carbon nanotubes, mica coated with antimony-doped tin oxide or indium tin oxide, or a mixture thereof.
 5. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from alkyl or aryl silane, alkyl or aralkyl group, hydroxyl group, carboxyl group, amine group, sulfonate group (—SO₃H), aldehydic group, quinoidal, fluorocarbon, or a combination thereof.
 6. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from a derivative of an azide compound selected from the group consisting of 2-azidoethanol, 3-azidopropan-1-amine, 4-(2-azidoethoxy)-4-oxobutanoic acid, 2-azidoethyl-2-bromo-2-methylpropanoate, chlorocarbonate, azidocarbonate, dichlorocarbene, carbene, aryne, nitrene, (R-)-oxycarbonyl nitrenes, where R=any one of the following groups,

and combinations thereof.
 7. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from an oxygenated group selected from the group consisting of hydroxyl, peroxide, ether, keto, and aldehyde.
 8. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from the group consisting of SO₃H, COOH, NH₂, OH, R′CHOH, CHO, CN, COCl, halide, COSH, SH, COOR′, SR, SiR′₃, Si(—OR′—)_(y)R′₃-y, Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is an integer equal to or less than 3, R′ is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, and combinations thereof.
 9. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from the group consisting of amidoamines, polyamides, aliphatic amines, modified aliphatic amines, cycloaliphatic amines, aromatic amines, anhydrides, ketimines, diethylenetriamine (DETA), triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxy adduct, phenolic hardener, non-brominated curing agent, non-amine curatives, and combinations thereof.
 10. The coating suspension of claim 1, wherein said chemically functionalized graphene comprises graphene sheets having a chemical functional group selected from OY, NHY, O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, and Y is a functional group of a protein, a peptide, an amino acid, an enzyme, an antibody, a nucleotide, an oligonucleotide, an antigen, or an enzyme substrate, enzyme inhibitor or the transition state analog of an enzyme substrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X, R′N⁺(R′)₃X⁻, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—) OR′, R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′, (C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than
 200. 